How can you determine if two (or more) fractions are equivalent. give an example.

Ametalworker has a metal alloy that is 30? % copper and another alloy that is 55? % copper. how many kilograms of each alloy should the metalworker combine to create 90 kg of a 50? % copper? alloy?

Use multiples to write two fractions equivalent to 7/9. 14/18, 8/10 6/8, 21/27 10/12, 28/36 14/18, 21/27

Can someone show me step by step how to do this?